1. Field of the Invention
Embodiments of the present invention generally relate to a gripping assembly for gripping tubulars. More particularly, the invention relates to a gripping apparatus for connecting wellbore tubulars on a drilling rig. More particularly still, the invention relates to a gripping apparatus including at least one redundant device to keep gripping members in contact with the tubular.
2. Description of the Related Art
In the construction and completion of oil and gas wells, a drilling rig is located on the earth's surface to facilitate the insertion and removal of tubular strings to and from a wellbore. The tubular strings are constructed and run into the hole by lowering a string into a wellbore until only the upper end of the top tubular extends from the wellbore (or above the rig floor). A gripping device, such as a set of slips or a spider at the surface of the wellbore, or on the rig floor, holds the tubular in place with bowl-shaped slips while the next tubular to be connected is lifted over the wellbore center. Typically, the next tubular has a lower end with a pin end, male threaded connection, for threadedly connecting to a box end, female threaded connection, of the tubular string extending from the wellbore. The tubular to be added is then rotated, using a top drive, relative to the string until a joint of a certain torque is made between the tubulars.
A tubular connection may be made near the floor of the drilling rig using a power tong. Alternatively, a top drive facilitates connection of tubulars by rotating the tubular from its upper end. The top drive is typically connected to the tubular by using a tubular gripping tool that grips the tubular. With the tubular coupled to a top drive, the top drive may be used to make up or break out tubular connections, lower a string into the wellbore, or even drill with the string when the string includes an earth removal member at its lower end.
An internal gripping device or spear may grip the inside diameter of a tubular to temporarily hold the tubular while building a string or rotating the string to drill. An internal gripping device is typically connected at an upper end to a top drive and at a lower end the internal gripping device includes outwardly extending gripping members configured to contact and hold the interior of the tubular in order to transmit axial and torsional loads. The result is a rotationally fixed assembly. The prior art gripping assemblies, however, are equipped with one primary actuator and one mechanical spring backup for setting the gripping member. Since the backup is a mechanical backup, it is prone to mechanical failure. Further, because the mechanical backup is simply a spring, there is no way to remotely monitor its condition.
There is a need for an improved gripping assembly having additional safety systems to prevent inadvertent disconnection of the string from the gripping apparatus. There is a further need for a safety system which utilizes a redundant actuator for the gripping apparatus. There is a further need for an integrated safety system between the gripping apparatus and a gripper on the rig floor.